[PATCH 1/2] compat: move unaligned helpers to bswap.h
From: Vicent Marti tan...@gmail.com
Commit d60c49c (read-cache.c: allow unaligned mapping of the
index file, 2012-04-03) introduced helpers to access
unaligned data. Let's factor them out to make them more
widely available.
While we're at it, we'll give the helpers more readable
names, add a helper for the ntohll form, and add the
appropriate Makefile knob.
Signed-off-by: Vicent Marti tan...@gmail.com
Signed-off-by: Jeff King p...@peff.net
---
Makefile | 7 +++
compat/bswap.h | 28
read-cache.c | 44
3 files changed, 47 insertions(+), 32 deletions(-)
diff --git a/Makefile b/Makefile
index 4136c4f..5711c0e 100644
--- a/Makefile
+++ b/Makefile
@@ -342,6 +342,9 @@ all::
# Define DEFAULT_HELP_FORMAT to man, info or html
# (defaults to man) if you want to have a different default when
# git help is called without a parameter specifying the format.
+#
+# Define NEEDS_ALIGNED_ACCESS if your platform cannot handle unaligned
+# access to integers in mmap'd files.
GIT-VERSION-FILE: FORCE
@$(SHELL_PATH) ./GIT-VERSION-GEN
@@ -1505,6 +1508,10 @@ ifneq (,$(XDL_FAST_HASH))
BASIC_CFLAGS += -DXDL_FAST_HASH
endif
+ifdef NEEDS_ALIGNED_ACCESS
+ BASIC_CFLAGS += -DNEEDS_ALIGNED_ACCESS
+endif
+
ifeq ($(TCLTK_PATH),)
NO_TCLTK = NoThanks
endif
diff --git a/compat/bswap.h b/compat/bswap.h
index c18a78e..80abc54 100644
--- a/compat/bswap.h
+++ b/compat/bswap.h
@@ -122,3 +122,31 @@ static inline uint64_t git_bswap64(uint64_t x)
#endif
#endif
+
+#ifndef NEEDS_ALIGNED_ACCESS
+#define align_ntohs(var) ntohs(var)
+#define align_ntohl(var) ntohl(var)
+#define align_ntohll(var) ntohll(var)
+#else
+static inline uint16_t ntohs_force_align(void *p)
+{
+ uint16_t x;
+ memcpy(x, p, sizeof(x));
+ return ntohs(x);
+}
+static inline uint32_t ntohl_force_align(void *p)
+{
+ uint32_t x;
+ memcpy(x, p, sizeof(x));
+ return ntohl(x);
+}
+static inline uint64_t ntohll_force_align(void *p)
+{
+ uint64_t x;
+ memcpy(x, p, sizeof(x));
+ return ntohll(x);
+}
+#define align_ntohs(var) ntohs_force_align((var))
+#define align_ntohl(var) ntohl_force_align((var))
+#define align_ntohll(var) ntohll_force_align((var))
+#endif
diff --git a/read-cache.c b/read-cache.c
index 33dd676..fa53504 100644
--- a/read-cache.c
+++ b/read-cache.c
@@ -1313,26 +1313,6 @@ int read_index(struct index_state *istate)
return read_index_from(istate, get_index_file());
}
-#ifndef NEEDS_ALIGNED_ACCESS
-#define ntoh_s(var) ntohs(var)
-#define ntoh_l(var) ntohl(var)
-#else
-static inline uint16_t ntoh_s_force_align(void *p)
-{
- uint16_t x;
- memcpy(x, p, sizeof(x));
- return ntohs(x);
-}
-static inline uint32_t ntoh_l_force_align(void *p)
-{
- uint32_t x;
- memcpy(x, p, sizeof(x));
- return ntohl(x);
-}
-#define ntoh_s(var) ntoh_s_force_align((var))
-#define ntoh_l(var) ntoh_l_force_align((var))
-#endif
-
static struct cache_entry *cache_entry_from_ondisk(struct ondisk_cache_entry
*ondisk,
unsigned int flags,
const char *name,
@@ -1340,16 +1320,16 @@ static struct cache_entry
*cache_entry_from_ondisk(struct ondisk_cache_entry *on
{
struct cache_entry *ce = xmalloc(cache_entry_size(len));
- ce-ce_stat_data.sd_ctime.sec = ntoh_l(ondisk-ctime.sec);
- ce-ce_stat_data.sd_mtime.sec = ntoh_l(ondisk-mtime.sec);
- ce-ce_stat_data.sd_ctime.nsec = ntoh_l(ondisk-ctime.nsec);
- ce-ce_stat_data.sd_mtime.nsec = ntoh_l(ondisk-mtime.nsec);
- ce-ce_stat_data.sd_dev = ntoh_l(ondisk-dev);
- ce-ce_stat_data.sd_ino = ntoh_l(ondisk-ino);
- ce-ce_mode = ntoh_l(ondisk-mode);
- ce-ce_stat_data.sd_uid = ntoh_l(ondisk-uid);
- ce-ce_stat_data.sd_gid = ntoh_l(ondisk-gid);
- ce-ce_stat_data.sd_size = ntoh_l(ondisk-size);
+ ce-ce_stat_data.sd_ctime.sec = align_ntohl(ondisk-ctime.sec);
+ ce-ce_stat_data.sd_mtime.sec = align_ntohl(ondisk-mtime.sec);
+ ce-ce_stat_data.sd_ctime.nsec = align_ntohl(ondisk-ctime.nsec);
+ ce-ce_stat_data.sd_mtime.nsec = align_ntohl(ondisk-mtime.nsec);
+ ce-ce_stat_data.sd_dev = align_ntohl(ondisk-dev);
+ ce-ce_stat_data.sd_ino = align_ntohl(ondisk-ino);
+ ce-ce_mode = align_ntohl(ondisk-mode);
+ ce-ce_stat_data.sd_uid = align_ntohl(ondisk-uid);
+ ce-ce_stat_data.sd_gid = align_ntohl(ondisk-gid);
+ ce-ce_stat_data.sd_size = align_ntohl(ondisk-size);
ce-ce_flags = flags ~CE_NAMEMASK;
ce-ce_namelen = len;
hashcpy(ce-sha1, ondisk-sha1);
@@ -1389,14 +1369,14 @@ static struct cache_entry *create_from_disk(struct
ondisk_cache_entry *ondisk,
unsigned int flags;
/* On-disk flags are just 16 bits */
- flags = ntoh_s(ondisk-flags);
+ flags = align_ntohs(ondisk-flags);
Re: [PATCH 1/2] compat: move unaligned helpers to bswap.h
Jeff King wrote: Commit d60c49c (read-cache.c: allow unaligned mapping of the index file, 2012-04-03) introduced helpers to access unaligned data. Let's factor them out to make them more widely available. While we're at it, we'll give the helpers more readable names, add a helper for the ntohll form, and add the appropriate Makefile knob. Weird. Why wasn't git broken on the relevant platforms before (given that no one has been setting NEEDS_ALIGNED_ACCESS for them)? Puzzled, Jonathan -- To unsubscribe from this list: send the line unsubscribe git in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: [PATCH 1/2] compat: move unaligned helpers to bswap.h
On Thu, Jan 23, 2014 at 11:41:18AM -0800, Jonathan Nieder wrote: Jeff King wrote: Commit d60c49c (read-cache.c: allow unaligned mapping of the index file, 2012-04-03) introduced helpers to access unaligned data. Let's factor them out to make them more widely available. While we're at it, we'll give the helpers more readable names, add a helper for the ntohll form, and add the appropriate Makefile knob. Weird. Why wasn't git broken on the relevant platforms before (given that no one has been setting NEEDS_ALIGNED_ACCESS for them)? Because most of our data structures support aligned access. Thomas mentioned this as a potential issue earlier, and I said in a re-roll cover letter: I did not include the NEEDS_ALIGNED_ACCESS patch. I note that we do not even have a Makefile knob for this, and the code in read-cache.c has probably never actually been used. Are there real systems that have a problem? The read-cache code was in support of the index v4 experiment, which did away with the 8-byte padding. So it could be that we simply don't see it, because everything is currently aligned. I think it was a bug waiting to surface if index v4 ever got wide use. -Peff -- To unsubscribe from this list: send the line unsubscribe git in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: [PATCH 1/2] compat: move unaligned helpers to bswap.h
Jeff King wrote: I think it was a bug waiting to surface if index v4 ever got wide use. Ah, ok. In that case I think git-compat-util.h should include something like what block-sha1/sha1.c has: #if !defined(__i386__) !defined(__x86_64__) \ !defined(_M_IX86) !defined(_M_X64) \ !defined(__ppc__) !defined(__ppc64__) \ !defined(__powerpc__) !defined(__powerpc64__) \ !defined(__s390__) !defined(__s390x__) #define NEEDS_ALIGNED_ACCESS #endif Otherwise we are relying on the person building to know their own architecture intimately, which shouldn't be necessary. Meanwhile, as mentioned in the other message, I suspect the NEEDS_ALIGNED_ACCESS code path is broken for aggressive compilers anyway. Looking more. Thanks, Jonathan -- To unsubscribe from this list: send the line unsubscribe git in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: [PATCH 1/2] compat: move unaligned helpers to bswap.h
On Thu, Jan 23, 2014 at 12:08:04PM -0800, Jonathan Nieder wrote: Jeff King wrote: On Thu, Jan 23, 2014 at 11:56:43AM -0800, Jonathan Nieder wrote: In that case I think git-compat-util.h should include something like what block-sha1/sha1.c has: #if !defined(__i386__) !defined(__x86_64__) \ !defined(_M_IX86) !defined(_M_X64) \ !defined(__ppc__) !defined(__ppc64__) \ !defined(__powerpc__) !defined(__powerpc64__) \ !defined(__s390__) !defined(__s390x__) #define NEEDS_ALIGNED_ACCESS #endif Otherwise we are relying on the person building to know their own architecture intimately, which shouldn't be necessary. Yeah, I agree it would be nice to autodetect. The nice thing is that false positives are harmless, modulo slowing down git a little if the compiler doesn't figure out how to optimize the NEEDS_ALIGNED_ACCESS codepath when on an unlisted platform that doesn't, in fact, need aligned access. OK, I'll refactor the knob. -Peff -- To unsubscribe from this list: send the line unsubscribe git in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: [PATCH 1/2] compat: move unaligned helpers to bswap.h
Jeff King wrote: On Thu, Jan 23, 2014 at 11:56:43AM -0800, Jonathan Nieder wrote: In that case I think git-compat-util.h should include something like what block-sha1/sha1.c has: #if !defined(__i386__) !defined(__x86_64__) \ !defined(_M_IX86) !defined(_M_X64) \ !defined(__ppc__) !defined(__ppc64__) \ !defined(__powerpc__) !defined(__powerpc64__) \ !defined(__s390__) !defined(__s390x__) #define NEEDS_ALIGNED_ACCESS #endif Otherwise we are relying on the person building to know their own architecture intimately, which shouldn't be necessary. Yeah, I agree it would be nice to autodetect. The nice thing is that false positives are harmless, modulo slowing down git a little if the compiler doesn't figure out how to optimize the NEEDS_ALIGNED_ACCESS codepath when on an unlisted platform that doesn't, in fact, need aligned access. In other words, it would work out of the box for everybody. -- To unsubscribe from this list: send the line unsubscribe git in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
